1. Field of the Invention
The present invention relates to hard disk drives. More particularly, the present invention relates to a method for managing defective data sites encountered during operation of the disk drive through a single defect management table.
2. Description of the Related Art
Hard disk drives store large volumes of data on one or more disks mounted on a spindle assembly. Disk drives employ a disk control system for interfacing with a host (e.g., a computer) to control the reading and writing of data on a disk. Each disk includes at least one disk surface which is capable of storing data. On each disk surface, user data is stored in data sectors (i.e., data sites) organized in concentric circular tracks between an outside diameter and an inside diameter of the disk.
As a result of the manufacturing process, defective data sites may exist on the disk surfaces of the disk drive. These defective data sites are conventionally termed "primary" defects. A defect discovery procedure is performed to locate these defects and mark them out as defective locations on the disk surface which are not available for use. A typical defect discovery procedure includes writing a known data pattern to the disk surface and subsequently reading the data pattern from the disk surface. Defective data sites are identified by comparing the data pattern read from the disk surface with the known data pattern written to the disk surface.
Following the defect discovery procedure, defective data sites are written to a primary defect list (PLIST). The primary defect list is used during formatting of the disk surface to generate a primary defect management table. Once identified in the primary defect management table, the defective data site may not be used for storing data and are passed over or "skipped" during disk drive operations.
Defective data sites encountered after formatting the disk surface are known as "grown defects" or "secondary defects". Grown defects often occur in locations adjacent to defective data sites found during defect discovery. Grown defects are also written to a list, known as the grown defect list (GLIST), similar to that utilized for the primary defects. Grown defects encountered during the operation of the disk drive are added to a secondary defect management table. The secondary defect management table is utilized along with the primary defect management table during the operation of the disk drive for the identification of defective data sites on the disk surface. The defective data sites residing within the secondary defect management table are reassigned or "vectored" (i.e., mapped via an index pointer) to spare data site locations via a cross-reference entry (cylinder number, head number, and data sector number).
Thus, in prior art reassignment schemes, separate defect management tables are maintained for skipped data sites and reassigned data sites. The primary defect management table typically contains a list of data site addresses to be avoided during operation. In contrast, the secondary defect management table typically contains multiple cross-reference entries of data site reassignments, where each entry contains a defective data site address and a corresponding spare data site address which contains the reassigned data from the defective data site address. Due to limited bandwidth and operational memory, it is desirable to minimize the use and complexity of defect management tables which are active during read/write operations. The maintenance and use of two separate defect management tables during the operation of the disk drive results in operational inefficiencies.
There is a continuing need therefore for a defect management scheme which minimizes the operational inefficiencies while dealing effectively with defective data sites which are discovered during disk operations.